How do you set this problem up on paper? I came up with a different answer.but mine was exactly 2x your answer.
I figured that every time I drove 20 miles in the car vs the truck I would save 1 gallon of fuel, so I used 20 over 3.50= X over 10,000.them I cross multiplied and figured out X.
X = 57,143.
Did I do this wrong?

You are correct. You are saving 17.5 cents per mile driven by driving the car. $10,000 / .175 = 57,143

I have a truck that gets 10mpg.
I buy a car that gets 20mpg.
I paid $10,000 for the car.
Gas is always $3.50/gallon.
How many miles do I need to drive before the car starts to save me money?

The way you state your question, (and I think what you are really wanting to know is: that if my MPG go from 10mpg to 20mpg how long will it take me to save $10k in gas.

If that is the case then, basically you are doubling you MPG so cost per/month in fuel will decrease by half. So say you drive 1000 miles per month which noramlly would cost you $350 now it will cost you $175.

A savings of $175 per month.

However if you leave you question the way its stated in Post #1, then the person that said drive it 1 mile it will save you money is correct.

Quote:

Originally Posted by amc78cj7

miles = 10 miles per gallon / $3.50 per gallon x $10,000 = 28,571.43 miles

Winner winner chicken dinner ^^^^^^^.

The reason you got twice this answer Curbdog, is because you used a factor of 20mpg. You need to use the difference between the 2 wihich is 10mpg.